Here's why:

* Chromosomes are made of DNA: Chromosomes are essentially long, tightly coiled strands of DNA. They contain the genes that determine our traits.

* Nuclear DNA: The majority of DNA in a cell is found within the nucleus, organized into chromosomes.

* Mitochondrial DNA: A small amount of DNA is also found in the mitochondria, organelles responsible for energy production. However, the amount of mitochondrial DNA is significantly less than the DNA found in chromosomes.

So, while there's a small amount of DNA in the mitochondria, the vast majority of a cell's DNA is contained within its chromosomes.